Simulated Cervical ARFI

Abstract

<p>Every day, 1,300 children in the U.S. and an additional 34,000 children worldwide are born prematurely. This study acts as a feasibility study for a proposed ultrasonic technique for the identification of preterm birth risk factors using an acoustic technique known as Acoustic Radiation Force Impulse (ARFI) imaging. A 3D finite element model was constructed to optimize transducer ARFI parameters in a layered cervix structure prior to clinical evaluation. The transducer model optimized in this study was the AcuNav^TM (Siemens Medical Solutions, Mountain View, CA). Cervix model structural geometry and material properties were varied according to anticipated pregnancy induced property fluctuation. Transmitted ARFI acoustic fields were generated by applying a Field II derived pulse to the 3D model[15]. Optimization procedures were performed in the following order: focal depth evaluation, transmit frequency optimization, effect of material property variation and the application of ARFI shear wave speed calculation algorithms to a layered cervical structure. Results indicated that ARFI evaluation of a layered cervix structure was most feasible using an 8MHz transmit frequency in the focal range of 5-10mm axial depth. It was observed that material property estimation errors were most likely when ARFI excitations were focused near a material boundary. A phenomenon was noted where shear waves initiated in stiffer media were slowed as a function of their relative proximity to a more compliant medium. Overall, these simulation studies demonstrate that ARFI shear wave imaging in the cervix is feasible; a model has been developed that can be used to evaluate the accuracy of shear stiffness estimates in the cervix to help address the important clinical problem of premature cervical ripening.</p>